#include <bits/stdc++.h>
using namespace std;

ifstream fin("deque.in");
ofstream fout("deque.out");

int dq[5000005],v[5000005];

int main()
{
    int n,k,i,x;
    int st=1,dr=0;
    long long sum=0;
    fin>>n>>k;
    for(i=1;i<=n;i++)
    {
        fin>>v[i];
        if(i-k==dq[st])
            st++;
        while(st<=dr&&v[i]<=v[dq[dr]])
            dr--;
        dq[++dr]=i;
        if(i>=k)
            sum+=v[dq[st]];
    }
    fout<<sum;
    return 0;
}